Kinetic Analysis and Characterization of Epoxy Resins ... - FedOA

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Results and Discussion 150 and microwave cured for the evaluation of flexural elastic modulus and the stressstrain curves. In these test a beam of the specimen is supported at two points and loaded in the midpoint. For this purpose specimens of rectangular shape of size reported in Table 3.27 have been used. Flexural Test Specimen Size Length Width Thickness ≈ 12 cm ≈ 1cm ≈ 2mm Table 3.27: Size of specimens used for flexural tests. The load has been applied on the specimen with a rate of crosshead motion calculated with the following relation: R= ZL2 6d (3.33) where R [mm] is the rate of crosshead motion, L [mm] is the support span, d [mm] is the depth of the beam and Z [mm/mm/min] the rate of straining of the outer fiber. Z shall be equal to 0,01. The loading nose and the supports have been aligned so that the axes of the cylindrical surfaces are parallel and the loading nose is midway between the supports. The test has been interrupted when the 5% of deformation of the specimens has been reached. During the test simultaneous load-deflection data have been measured. 150
Results and Discussion 151 3.6.1 Stress-Strain Plot The investigation of flexural properties of the epoxy system has been performed through analysis of stress-strain curves during three point bending test on specimens cured in both the way. The flexural stress may be calculated for any point on the load-deflection curve by means of the following equation: σ f = 3PL 2bd 2 (3.34) where σ f [MPa] is the stress in the outer fibers at midpoint, P [N] is the load at a given point on the load-deflection curve, L [mm] is the support span, b [mm] the width of the beam tested and d the depth. The flexural strain is the nominal fractional change in the length of an element of the outer surface of the test specimen at midpoint, where the maximum strain occurs. It may be calculated for any deflection using the following equation: ɛ f = 6Dd L 2 (3.35) where ɛ f [mm/mm] is the strain in the outer surface, D [mm] is the maximum deflection of the center of the beam, L [mm] is the support span and d [mm] the depth. In Figure 3.40 a comparison of stress-strain curves of the best specimens conventionally and microwave cured is shown. The stress necessary for achieve a given strain is much higher for specimens microwave cured than that thermally crosslinked. Moreover for samples conventionally polymerized the elongation at break is greater. Plasticization phenomena can be occurred. The tangent modulus of elasticity, often called modulus of elasticity, is the ratio, within the elastic limit, of stress to corresponding strain. It is calculated by 151
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UNIVERSITA’ DEGLI STUDI DI NAPOLI
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3 I thank all the lecturers of PhD
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5 Microwaves are electromagnetic ra
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CONTENTS 7 1.8.1 DielectricProperti
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CONTENTS 9 4 Conclusions and Outloo
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LIST OF TABLES 11 3.2 Average value
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List of Figures 1.1 Diglycidylether
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LIST OF FIGURES 15 2.23 Onset tempe
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LIST OF FIGURES 17 3.38 Comparison
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Introduction 19 cannot be melted an
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Introduction 21 • bismaleimides;
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Introduction 23 cold solders, casti
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Introduction 25 Average Properties
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Introduction 27 In Figure 1.4 n can
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Introduction 29 ducts and it genera
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Introduction 31 tween current-carry
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Introduction 33 that describe the p
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Introduction 35 1.3.5 Lorentz Force
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Introduction 37 Figure 1.11: Electr
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Introduction 39 Even microwaves can
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Introduction 41 production requirem
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Introduction 43 fect of the electro
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Introduction 45 following different
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Introduction 47 Debye equations bas
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Introduction 49 Although these mode
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Introduction 51 materials that have
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Chapter 2 Experimental In this chap
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Experimental 55 Characteristic Note
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Experimental 57 If the oven is used
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Experimental 59 In monomodal applic
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Experimental 61 Figure 2.5: Right s
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Experimental 63 Figure 2.8: Front v
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Experimental 65 regardless of the a
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Experimental 67 • The number of t
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Experimental 69 Figure 2.11: Surfac
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Experimental 71 Figure 2.12: Repeti
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Experimental 73 From the Figure 2.1
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Experimental 75 in the centre of th
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Experimental 77 not read the water
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Experimental 79 Test number 1 2 3 4
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Experimental 81 Figure 2.19: Plot o
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Experimental 83 2.5 Datalogger This
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Experimental 85 same reason a wood
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Experimental 87 Material Behaviour
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Experimental 89 in function of the
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Experimental 91 2.6.3 Influence of
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Chapter 3 Results and Discussion Th
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Results and Discussion 95 There is
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Results and Discussion 97 Figure 3.
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Page 165 and 166: Appendix A A Brief History of Micro
Page 167 and 168: A Brief History of Microwave Oven 1
Page 169 and 170: Bibliography [1] W. Callister, “M
Page 171 and 172: BIBLIOGRAPHY 171 [19] P. I. Karkana
Page 173: BIBLIOGRAPHY 173 [34] K. D. V. Pras
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